DISCRETE AND CONTINUOUS SIMULATION OF MANUFACTURING
PROCESSES
DISKRÉTNA A SPOJITÁ SIMULÁCIA VÝROBNÝCH PROCESOV
Ing. Maroš Fill, prof. Ing. Gabriel Fedorko PhD.
Technická univerzita v Košiciach
[email protected]
Abstract
This paper deals with simulation capabilities specified for discrete and continuous
manufacturing processes using the object-oriented (block-oriented) software tools called
Extend and Plant Simulation. Introduction of this paper describes differences between the
discrete and continuous simulation and their mutual comparison, further part presents a
possibility of simulation of manufacturing processes using the simulation program Extend and
then it is pointed out innovation of simulation using the Plant Simulation.
Abstrakt
Príspevok sa zaoberá možnosťami simulácie diskrétnych a spojitých výrobných procesov
pomocou objektovo orientovanými (blokovými) softvérovými nástrojmi Extend a Plant
Simulation. Úvod príspevku sa venuje rozdielu a porovnaniu diskrétnej a spojitej simulácie, ďalej
príspevok predstavuje možnosti simulácie výrobných procesov pomocou simulačného programu
Extend a následne poukazuje na inovácie simulácii pomocou programu Plant Simulation.
Key words
Discrete simulation, Continuous simulation, Extend, Plant Simulation
Klíčová slova
Diskrétne simulácie, kontinuálne simulácie, softvérové nástroje Extend a Plant Simulation
INTRODUCTION
The simulation software products are such useful tools, which are able to test various
decisions using a simulation model, to evaluate the individual production capacities and
duration of working operations, together with evaluation of other parameters in the given
production system as well as they are useful for elimination of an unfavourable possibility to
involve some undesirable change into the manufacturing process. [1] Nowadays, creation or
development of simulation software is a simple task and a user-friendly process because it
requires only knowledge of simulation blocks, their properties and application possibilities.
Creation of a simulation model by means of these blocks and the following simulation process
is such task, which can be mastered by a standard user of the up-to-date PC-technology. There
are presented in this paper two block-oriented (or subject-oriented) software applications that
are specified for simulation of discrete and continuous manufacturing processes.
COMPARISON OF CONTINUOUS AND DISCRETE SIMULATION
The next Table 1 describes the basic differences between the continuous and
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discrete simulation. Such tabular comparison of the individual characteristic features
and differences can be helpful for users during their decision-making process
concerning a question about model, which should be chosen and applied for the given
simulated system. [2]
Tab. 1 Comparison of continuous and discrete simulation [2]
Factors
Continuous Simulation
Discrete (Discontinuous) Simulation
What will be
simulated?
Flows (materials, roughs)
Discrete items (things, needs, requirements
Characteristics
Simulation is typical for flows, i.e.
calculation process is sequential
Application of the individual values, which
are applied in the whole simulated system
Time step
Interval between the individual time
steps is the same
Time step is changing according to
occurrence of the individual occasions
Queueing
Flows are managed by the FIFO system
only
There are applied various managing
systems, e.g. the FIFO, LIFO, etc.
Routing of
flows
The flows can be situated in the same
time at various points simultaneously
Dominant is the first suitable flow, which
can be situated at one point only in the
given time
Statistical
details
There are applied general statistics only
that are describing the system
Every requirement can by evaluated
individually
General
application
Scientific branches: biology, chemistry,
physics, electronics, control systems,
artificial intelligence systems, dynamic
systems.
Manufacturing, services, business
processes, computer networks, phone
networks, complex systems
SIMULATION LANGUAGE EXTEND
The simulation language EXTEND belongs into a group of simulation languages that
are able to perform both the discrete and continuous simulation process. From this reason the
EXTEND is a widely used simulation tool, which is suitable and specified for the platforms
PC-IBM and Macintosh.
The simulation language EXTEND is a product of the company Imagine That,
Inc. USA. This company offers the EXTEND in the next four different versions with
various application possibilities or various number of blocks developed for creation o f
the simulation models: EXTEND CP, EXTEND OR, EXTEND Industry and EXTEND
Suite. [2]
DISCRETE MODELS AND SIMULATION USING THE SIMULATION
LANGUAGE EXTEND
The discrete simulation (Fig.1) should be applied in order to simulate the main kinds
of the bulk-service systems, i.e. the simple, serial and parallel bulk-service system. The
blocks required for building of the discrete simulation models are at disposal in the library
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„Discrete Event“. Together with this library it is also necessary to open another library
„Plotter“, which is specified for illustration of the simulation behaviour and the results. This
illustration is presented in the form of tables and graphs. The library „Discrete Event“
contains several blocks with various application possibilities in order to create the simple
discrete simulation models. The most important blocks are: „Executive, Generator, Queue,
Activity and Exit“. [2]
Fig. 1
Discrete model Extend [2]
CONTINUOUS MODELS AND SIMULATION IN THE SIMULATION
LANGUAGE EXTEND
The next application part of the simulation language EXTEND is oriented into the area
of a continuous simulation. The main difference between the discrete and the continuous
simulation consists in a fact that in the case of the continuous simulation there are obtained
values or results from the simulated system in every time moment, even at that time when the
system remains without a change.
The continuous simulation in the simulation language EXTEND is performed using a
discrete time behaviour with the fixed time step, i.e. during the continuous simulation the time
behaviour is recorded always in the same time intervals, also without any change in the
simulated system. If the fixed time step value is small enough, then the time behaviour of the
simulation process is very similar to the continuous time behaviour.
Application of the continuous simulation (Fig.2) is relevant for biology, chemistry,
physics, electronics and economy as well as for the control systems, systems of artificial
intelligence and for dynamic systems.
In order to generate the basic simulation models within the framework of a continuous
simulation it is necessary to know the blocks from the library “Generic”. [2]
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Fig. 2
Continuous model Extend [2]
PLANT SIMULATION
The Plant Simulation (Fig. 3) is standard software used for simulation of very complex
production systems and managing strategies. This software simulation tool is characterised by
the object-oriented, graphical and integrated simulation or animation of the systems and
company processes. It is an important part and basic tool of a digital factory from the Siemens
PLM software portfolio. [3]
Fig. 3
Model in the Plant Simulation [4]
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The Plant Simulation enables to generate a simulation model of the given
production/assembly process and to test influence of changes in the manufacturing process on
the monitored parameters. An advantage of this process is a possibility to use a drawing
technical documentation as a base for arrangement of the individual elements or objects in the
existing or planned production plant. It enables to solve the next tasks:

to determine influences of changes in the manufacturing programmes
on the production and assembly equipment,

to test priority rules during scheduling of production,

to define storage capacities,

to verify influence of production and transport portion on workflow,

to determine time interval necessary for start-up of new
product manufacture,

to define a total production output of the plant or its part.
SIMULATION OF LOGISTIC PROCESSES – TRANSPORT AND STORAGE
An advantage of dynamic simulation is implementation of dynamics into the proposed
static processes. Monitoring of movement is important in the area of material transport within
the framework of external or internal transportation. The Plant Simulation enables to
assembly the simulation model of external and internal logistic systems and to verify
dynamically the systems before implementation of them into the real operation. Therefore the
dynamic simulation is applied in the next areas predominately:

testing of changes in the transport system and their influence on the
production/assembly system,

testing and evaluation of the various material supply systems,

testing of changes in the applied transport equipment with regard to
the given system capacity,

testing of changes in the transport task priorities with regard to the
production,

monitoring of influences of the crossroads and nodal points on the
transport equipment utilisation,

monitoring of random event influence – failures and changes – on the
total storage capacity in the given plant. [5]
SIMULATION OF HUMAN SOURCE DEMAND [5]
As it was mentioned already, the Plant Simulation contains a large amount of the
specialised modules. One of them is the special modulus developed for the simulation of
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human activities (Fig. 4). Everyone source, which is used in the company, i.e. also the human
work, is a limited source. Therefore the given software provides simulation of persons like
simulation of sources that are able to perform the following activities:

operating of equipment,

manipulation of products,

setting-up activities and maintenance activities .
Fig. 4
Simulation of human sources in the Plant Simulation [5]
PLANT SIMULATION AND INTERCONNECTION WITH SAP
A possibility of intuitive and fast data transfer between the central company software
SAP and the simulation software Plant Simulation is a necessity nowadays.
After a primary simulation of the individual workplaces and plants the data concerning
production are exported from the company software to the simulation model. The required
data are transferred through the central database of the company in order to perform the
discrete simulation. Another possibility of data transfer is exporting of data in a structured
form by means of the created Excel tables that are representing subsequently the main source
of data used for the simulation process control. [6]
VISUALISATION
The Plant Simulation enables to illustrate manufacturing sequences using the 2D and
3D visualisation. The 3D-visualisation (Fig.5) is useful predominately as a sale tool or for inhouse communication of the planned measures. Furthermore, it enables to present a whole
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concept of the given system in a virtual, interactive surrounding. [4] The 3D-visualisation is
created and saved in the standard format JT. The CAD-applications (e.g. NX, Solid Edge) are
able to export their models in this format.
Fig. 5
Visualisation in the Plant Simulation [7]
CONCLUSION
On the present there are various possibilities how to simulate various kinds of the
production processes. One of the possibilities is application of the software Extend. The
simulation language Extend belongs to a group of such simulation languages, which are able
to perform the discrete and continuous simulation. The Extend enables to create simulation of
the production process very simply and quickly using the individual blocks that are selected
from a large amount of the libraries offered by the Extend itself. It also offers visualisation of
the processes in a logistic model or in a virtual surrounding; it is able to discover possible
hidden failures in the production process, to investigate potential influences of the system
modifications and to optimise the individual activities performed inside of the production
process, as well.
The Plant Simulation is a standard software tool, which was developed for the
simulation of very complicated production systems and managing strategies. The main
characteristic feature of this simulation tool is the object-oriented, graphical and integrated
modelling as well as simulation and animation of the systems and company processes. It is an
integrated part and a basic tool of a digital factory, together with implemented ability to
simulate and to analyse the multi-level systems, human source needs, energy consumption,
data transfer from the SAP system and to offer the 2D or 3D-visualisation of the production
sequences, too.
This article is a part from solution of the grant projects VEGA 1/0922/12, VEGA 1/0258/14
and APVV SK-CZ-2013-0169.
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LITERATURE
[1] DLOUHÝ, . a kol.: Simulace podnikových proces . Brno: Computer Press, a.s., 2007,
s. 201, ISBN 978- 80- 251- 1649- 4.
[2] STRAKA, . Diskrétna a spojitá simulácia v simulačnom jazyku Extend. Košice: Edixné
stredisko/A S, Technická univerzita v Košiciach, fakulta BERG, ISBN 978-80-8073-884-6,
99 s.
[3] Plant Simulation, [cit. 2015-2-20] Dostupné na internete:
http://www.innov8.sk/plant-simulation/
[4] Platn Simulation – model [cit. 2015-3-15] Dostupné na internete:
http://www.simplan.de/images/stories/software/Plant_Simulation.jpg
[5] Priemyselné inžinierstvo – Plant Simulation, [cit. 2015-2-20] Dostupné na internete:
http://www.priemyselneinzinierstvo.sk/?page_id=1695
[6] Plant Simulation – SAP, [cit. 2015-3-15] Dostupné na internete:
http://www.sova.sk/sk/produkty/tecnomatix/suvisiace-clanky/planovanie-vyroby-s-plantsimulation
[7] Plant Simulation – Vizualizácia [cit. 2015-3-15] Dostupné na internete:
http://4dsysco.com/siemens-plm/tecnomatix/tecnomatix-factorycad/
Reviewers:
prof. Ing. Vladimír Strakoš, DrSc., VŠLG Přerov,
Ing. Stanislav Honus, PhD., UTB Zlín.
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